i dont know ho to do this freecodecamp javascript calculator

Question

help !! the console tells me x13. If 2 or more operators are entered consecutively, the operation performed should be the last operator entered (excluding the negative (-) sign. The sequence"5-5"=should produce an output of"-25"expected'-5'to equal¹-25' AssertionError:The sequence"5-5"=should produce an output of"-25"expected'-5'to equal

I try to use regex because someone tells me I should do that but I don't know how. I do 15 right but one is wrong and I can't pass this test :(

https://codepen.io/mikaelamattos/pen/RwQGeXe

let trailingResult = 0;

let operationOptions = ['divide', 'multiply', 'subtract', 'add'];
let workingOperation = "";

function updateDisplay(input) {
  let display = document.getElementById("display");
  let secondaryDisplay = document.getElementById("secondaryDisplay");

  if (display.innerHTML === "0" && operationOptions.indexOf(input) === -1) {
    if (input === "decimal") {
      display.innerHTML = "0.";
    } else if (input === "negative-value") {
      if (display.innerHTML.indexOf("-1") === -1) {
        display.innerHTML = "-" + display.innerHTML
      } else if (display.innerHTML.indexOf("-1" > -1)) {
        display.innerHTML = display.innerHTML.slice(1, display.innerHTML.length);
      }
    } else {
      display.innerHTML = input;
    }
  } else if (operationOptions.indexOf(input) >= 0) {
   

    if (trailingResult === display.innerHTML) {
      
      workingOperation = input;
    } else if (workingOperation === "") {
    
      workingOperation = input;
      trailingResult = display.innerHTML;
      secondaryDisplay.innerHTML = trailingResult;
      display.innerHTML = 0;
    } else {
      // Dealing with a set operand
      // console.log(display.innerHTML, " Dealing with set operand");
      trailingResult = calculate(trailingResult, display.innerHTML, workingOperation);
      secondaryDisplay.innerHTML = trailingResult;
      display.innerHTML = 0;
      workingOperation = input;
    }
  } else if (input === "equals") {
    display.innerHTML = calculate(trailingResult, display.innerHTML, workingOperation);
    trailingResult = 0;
    workingOperation = "";
    secondaryDisplay.innerHTML = trailingResult;
  } else if (input === "decimal") {
    // console.log('decimal clicked');
    if (display.innerHTML.indexOf(".") === -1) {
      display.innerHTML += ".";
    }
    // console.log("decimal skipped because decimal already in number.");
  } else if (input === "negative-value") {
    // console.log("negative-value selected");
    if (display.innerHTML.indexOf("-1") === -1) {
      display.innerHTML = "-" + display.innerHTML
    } else if (display.innerHTML.indexOf("-1" > -1)) {
      display.innerHTML = display.innerHTML.slice(1, display.innerHTML.length);
    }
  } else {
    display.innerHTML += input;
  }
  
}

function clearDisplay() {
  let display = document.getElementById("display");
  let secondaryDisplay = document.getElementById("secondaryDisplay");
  trailingResult = 0;
  display.innerHTML = 0;
  secondaryDisplay.innerHTML = trailingResult;
}

function calculate(firstNumber, secondNumber, operation) {
  let result;
  firstNumber = parseFloat(firstNumber);
  secondNumber = parseFloat(secondNumber);
  switch(operation) {
    case "add":
      
      result = firstNumber + secondNumber;
      break;
    case "subtract":
      
      result = firstNumber - secondNumber;
      break;
    case "multiply":
     
      result = firstNumber * secondNumber;
      break;
    case "divide":
      
      result = firstNumber / secondNumber;
      break;
    default:
      console.log("Calculate switch statement missed something");
  }
  return result.toString();
}